Conventional well-known method for sterilizing an object such as medical instrument includes applying heat or pressure from a source of high pressure steam, dry heat, electromagnetic radiation, hydrogen peroxide, gas plasma, or EOG gas.
The conventional method may be inapplicable to the object which can be damaged by heat or pressure. For example, the high pressure steam or the high temperature dry heat may be inapplicable to some objects. Also, the electromagnetic radiation may be inapplicable to other objects such as hollow metal or plastic composite material. Although the EOG gas sterilization may be applicable to any object irrespective of its material, it needs a considerable time for aeration procedures for the purpose of toxicity removal, which decreases the operational availability of the practical sterilizer.
One conventional solution that may solve those problems is a gas plasma sterilization method. For example, the method uses a sterilant containing hydrogen peroxide which is brought into contact with every surface portion of the object which has been washed and then dried completely. One known drying technique which may be used in the plasma gas sterilization is placing the object in a sterilization container, decompressing the interior of the container to vaporize residual water on the object, and then pumping to exhaust the generated vapor into the atmosphere and thereby to dry the object and the interior of the container.
Patent Document 1, for example, discloses a sterilization method using the technique, in which the interior of the object containing container is decompressed to about 40 to 200 Pa which is considered to be most advantageous for the generation of plasma within the container to vaporize the residual water on the object. Specifically, in this process, the vaporization of the residual water on the object loses its calories. Then, the object is heated at the generation of plasma within the interior of the container at a reduced pressure of about 40 to 200 Pa. Further, heat is transferred from the high-temperature container to the object through air introduced at the restoring of the pressure in the container to an atmospheric pressure or a quasi-atmospheric pressure (pressure which is close to the atmospheric pressure), increasing the temperature of the object and the residual water. Subsequently, a process for depressurizing the interior of the container to about 40 to 133 Pa and thereby to vaporize the residual water on the object is repeated at least twice.